Unidentified mechanisms cause the blood vessels in skeletal muscle and other organs to actively respond to changes in arterial pressure so that organ blood flow remains relatively constant despite pressure variations. The purpose of the proposed project is to identify the mechanism or mechanisms responsible for this autoregulatory phenomenon. At present, support is divided between a myogenic theory and a metabolic theory of autoregulation in skeletal muscle. Whereas previous studies have concentrated on the steady state aspects of autoregulation, I propose to concentrate on the dynamic or transient aspects of autoregulation. Preliminary experiments indicate that the vascular response to variation in arterial pressure depends upon the rate of pressure variation and, moreover, that muscle exercise greatly alters how muscle vessels react to changes in pressure. The rate-sensitive aspects of autoregulation will be characterized by measuring muscle flow responses to sinusoidal arterial pressure changes of different speeds. Control Theory techniques will be used in the data analysis. The nature of the autoregulatory mechanisms will elucidated by identifying what exercise related factors alter the dynamics of autoregulation. The effects of alterations in tissue PO2, tissue PCO2, plasma potassium ion concentration, average muscle flow, and average vascular tone will be studied. Mathematical model formulation of autoregulation will be used throughout the study to assist in determining which theory of autoregulation-or combination of theories-is consistent with the new experimental data on the dynamics of autoregulation.